The hernia follows the obturator canal, a defect between the superior pubic ramus and the obturator membrane which normally transmits only the obturator nerve and vessels. The sac then spreads out deep to the adductor muscles in the groin, where it is difficult to detect clinically. The sac usually contains small bowel, often as a Richter's type hernia but occasionally including the complete circumference; less commonly omentum, colon, fallopian tube, ovary, or bladder are found. Strangulation is common because of the rigid neck to the sac.

The majority of these hernias occur in elderly women who have recently lost weight. Sometimes straining because of constipation or other factors appears to be the immediate precipitating cause. The higher incidence in women is probably due to the wider pelvis, which changes the angle of the obturator canal.

Most patients present with acute groin pain; some also have abdominal symptoms, ranging from small bowel obstruction to mild and obscure discomfort. Approximately one-third report similar episodes in the past. The diagnosis is usually made during laparotomy for small bowel obstruction rather than preoperatively, mainly because the diagnosis is not entertained and the hernia itself difficult to palpate. Even if the correct diagnosis is suggested and the pathognomonic signs listed below are sought, they are positive in fewer than 50 per cent of cases.

1.Howship-Romberg sign—pain radiating to the medial thigh on extending, internally rotating, or adducting the hip.

2.Loss of the adductor reflex due to compression of the obturator nerve.

3.A hernial sac palpable as a tender mass on vaginal examination.

4.Bruising below the medial part of the inguinal ligament due to bloodstained exudate from a strangulated hernia.

In cases treated electively, usually with obscure groin pain as their only symptom, herniography may demonstrate the sac. Ultrasound is sometimes helpful.

When the patient presents as an emergency with small bowel obstruction a laparotomy is advisable to allow bowel resection if necessary. Otherwise a preperitoneal approach is used. The hernia is found disappearing into the obturator canal and must be reduced by traction, the obturator canal being enlarged if necessary by incising posteromedial to the neck of the hernia, thereby avoiding damage to the obturator nerve. Bowel is resected if necessary, the sac inverted or excised, and its neck closed by suture. It may be possible to close the defect by direct suture but extra reinforcement is usually required. Bladder or non-absorbable Marlex mesh can be sutured across it.

There is a high mortality rate (13–40 per cent) in these patients because of their age, nutritional state, and coexistent diseases.

The transversus abdominis muscle becomes aponeurotic at the semilunar line which stretches from the ninth rib to the pubic tubercle. Superficial to this muscle lies the internal oblique muscle, which splits lateral to the rectus muscle to run both anterior and posterior to it. The posterior layer is densely adherent to the transversus abdominis and forms the posterior rectus sheath. The lateral border of rectus muscle lies a variable distance medial to the semilunar line and the transversalis aponeurosis between the two, known as the Spigelian fascia, is an area of potential weakness. Furthermore it has bands of fibrous tissue running transversely; between these are well defined defects. It is through such a defect that a Spigelian hernia emerges, passing between the fibres of overlying internal oblique muscle and spreading out deep to the external oblique muscle. The hernia usually lies lateral to the rectus sheath and extends out towards the iliac fossa (Fig. 1) 1441; occasionally it lies within the sheath alongside the rectus muscle (Fig. 2) 1442. Only rarely does it penetrate the external oblique muscle to lie subcutaneously. The Spigelian fascia is only present in significant width below the umbilicus, and most Spigelian hernias occur in this region.

The sac may contain small bowel, colon, or omentum and may, like the obturator hernia, be a Richter's type hernia with only part of the bowel circumference involved. The rigid neck formed by the fibrous bands make strangulation common and repair is indicated wherever possible.

The patient is usually over 50 years old and commonly female. The diagnosis is often difficult because the hernia is impalpable, especially in the plump patient, and the only symptoms are of obscure abdominal pain or small bowel obstruction. A mass with a cough impulse may be palpable in the iliac fossa when the patient is standing; this disappears on lying down. Twenty per cent of these hernias have strangulated at presentation and there is then a tender mass in the abdominal wall which may be difficult to differentiate from an abdominal wall haematoma, a muscle tear, or an intra-abdominal inflammatory mass, especially when associated with small bowel obstruction. However, in all cases there is localized tenderness over the neck of the hernia at the lateral margin on the rectus sheath.

Ultrasound and CT are equally useful in confirming the diagnosis. Herniography may give false-negative results and is of less use.

This is a straightforward procedure when following confident preoperative diagnosis and localization. A transverse incision is made over the site, and external oblique fibres are split to expose the sac which is opened to check bowel viability. The defect can be enlarged laterally or medially to improve access if small bowel resection is required, or in order to reduce sac contents. The sac is excised and the defect closed by direct suture. If there is doubt over the diagnosis or location of the hernia then a vertical midline incision is made and an extraperitoneal approach made to the edge of the rectus sheath, where the hernia should be found disappearing through the Spigelian fascial defect. The contents are reduced, the sac excised, and the defect closed by direct suture from the inside.

Massive incisional lumbar hernias often follow removal of an infected kidney with subsequent wound infection. These are the most common type of lumbar hernia; other forms occur infrequently.

In the area between the twelfth rib and the iliac crest a number of back and abdominal muscles come together and create an area of potential weakness. The likelihood of herniation depends on the extent of approximation or overlap of these muscles, and this is subject to individual variation. The area can be divided into the superior and inferior lumbar triangles. The inferior triangle (of Petit) is the usual site of congenital lumbar herniation, which accounts for 25 per cent of cases. The boundaries of this area are the iliac crest inferiorly, the latissimus dorsi muscle superomedially and the posterior boundary of the external oblique muscle superolaterally. Acquired hernias are rare in this area, except when both internal and external tables of iliac crest have been removed for bone grafting.

The superior lumbar triangle is formed by quadratus lumborum, the twelfth rib, and the internal oblique muscle. It is the usual site of acquired hernias due to trauma (surgery, penetrating injury) or infection, or of those occurring spontaneously.

These hernias contain small or large bowel or omentum and have wide necks, so are at little risk of strangulation.

Lumbar hernias usually occur in middle-aged men. They appear as a lumbar bulge that appears on standing and disappears on lying down, has a cough impulse, and over which bowel sounds may be heard. The only symptom is usually a dull ache.

Surgery can be performed by a posterior approach with the patient in the lateral position, or through an anterior retroperitoneal approach. The sac is emptied, inverted, and can usually be closed off. Repairing the muscle defect is rather more difficult. If the hernia is small it may be possible to coapt adjacent muscles with non-absorbable sutures, but in most cases this is inadequate. Marlex mesh can be laid across the defect, preferably on its deeper aspect via the anterior, retroperitoneal approach. Alternatively a posterior approach is made with an additional vertical incision from the hernia down over the buttock, where a flap of fascia lata and gluteus maximus is mobilized and rotated up to close the defect.

The hernia sac finds its way out from the pelvis through either the greater sciatic foramen, above or below the piriformis muscle, or more commonly through the lesser sciatic foramen. The sac then lies deep to the gluteus maximus, where it is well hidden unless it is large enough to protrude below the buttock crease.

This is usually made at the time of laparotomy for small bowel obstruction caused by the hernia. The bowel is seen disappearing out through a posterior pelvic defect, behind the broad ligament in women.

The contents of the sac are reduced, the neck of the sac is ligated, and the defect covered by fascia mobilized from the piriformis muscle.

Perineal hernias are uncommon. They occur through defects in the muscular pelvic floor and usually follow pelvic exenteration or abdominoperineal excision of the rectum. The hernial contents are usually small bowel or bladder and there are rarely associated symptoms.

The usual approach is transabdominal. Once small bowel and bladder have been mobilized out of the way the defect is closed with Marlex mesh. If there is potential for infection synthetic implants are best avoided; gracilis muscle can be transposed from the thigh to form a sling across the defect via a perineal approach.

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